1. Field of the Invention
The present invention relates to a motion assist device for assisting a user in motion.
2. Description of the Related Art
In recent years, there has been proposed a device which assists a user in walk motion by applying a torque around a joint (a hip joint, a knee joint or an ankle joint) of a leg with respect to the body of the user. A control system has been disclosed for this kind of the walk assist device to maintain autonomy in a walk guiding rhythm of the walk assist device while following the variation of the walk motion rhythm of the user (refer to Patent Document 1: Japanese Patent Laid-open No. 2004-73649).
However, in the device according to Patent Document 1, it is possible that a footstep or an angle of a leg joint becomes excessively great or small due to excessively insufficient assist force or excessively insufficient action distance thereof even though a walk assist rhythm of the walk assist device is appropriate. In other words, although the motion rhythm of the user for guiding the motion of the user is consistent with a desired motion rhythm, the assist force or the action distance for guiding the motion of the user may make a motion scale of the user deviate from a desired motion scale, which applies uncomfortable feeling or the like to the user. In this regard, there has bee disclosed a device capable of assisting a user in motion by matching the motion rhythm of the user to a desired motion rhythm thereof and matching the motion scale of the user to a desired motion scale thereof (refer to Patent Document 2: Japanese Patent Laid-open No. 2007-61217).
According to the device disclosed in Patent Document 2, on the basis of a first oscillator generated by determining the motion of the user, a second oscillator is generated to match the motion rhythm of the user to the desired motion rhythm. On the basis of the generated second oscillator, a model containing elastic elements such as a virtual spring or the like is used to generate an auxiliary oscillator and to apply to the user a torque according to the auxiliary oscillator to perform the control so as to prevent the motion scale of the user from deviating from the desired motion scale.
Meanwhile, it is desirable for the walk assist device to assist a user in walking by maintaining a balance between a motion rhythm and a motion scale of the user. In particular, when a user is performing a walk motion for the purpose of training, it is desirable to walk in such a way that an index value denoting the balance between the motion rhythm and the motion scale of the user, such as a walk ratio, approximates to a predefined reference value.
The device according to Patent Document 2 is configured to perform controls so as to keep the motion rhythm consistent with the desired motion rhythm and the motion scale consistent with the desired motion scale, however, the balance between the motion rhythm and the motion scale has not been taken into consideration. Therefore, it is possible that the balance may not be maintained between the motion rhythm and the motion scale due to the affection from the elastic element model.